In general, a dialysis machine is used as a substitute for the natural kidney functions of a human body. As such, the dialysis machine cleans the blood of the natural accumulation of bodily wastes and separates the wastes from the blood outside the body or extracorporeally. The separated wastes are discharged and the cleansed blood is returned to the body.
A dialysis machine uses a dialyzer to separate the wastes from the blood. The dialyzer includes a porous medium located within a closed housing which separates the housing into a blood compartment and a dialysate compartment. The blood removed from the patient flows through the blood compartment of the dialyzer. A prepared solution of dialysate is passed through the dialysate compartment of the dialyzer. The wastes from the blood pass through the medium by osmosis, ionic transfer or fluid transport into the dialysate and, depending upon the type of dialysis treatment, desirable components from the dialysate may pass in the opposite direction through the medium and into the blood. The transfer of the wastes from the blood into the dialysate cleanses the blood while allowing the desired components from the dialysate to enter the bloodstream.
The dialysate must be heated before it is passed through the dialyzer. Since the dialyzer functions as a heat exchanger, it is important that the dialysate be at approximately the patient's body temperature. The flow rate of dialysate is generally high enough that a substantial amount of electrical power is consumed by the heater to raise the temperature of the dialysate to body temperature. The required increase in temperature may be substantial since the major component of dialysate is water, and the entering water temperature may be relatively low, for example as low as 5 degrees C. If the heater does not supply an adequate amount of heat, the flow rate of the dialysate must be reduced to attain the desired temperature elevation. Reducing the flow rate of the dialysate may require a directly related reduction in the flow of blood, which may in turn extend the time required to complete the dialysis treatment.
Of course, the dialysis treatment can not begin until the dialysate temperature is raised to body temperature. The initial time required to heat the dialysate before the treatment begins is referred to as a warm-up time. The warm-up time normally starts after the patient is connected to the dialysis machine, and can seem relatively long to the patient.
Heaters are also used in dialysis machines to elevate the temperature of a cleaning solution during a cleaning and disinfecting procedure applied prior to using the dialysis machine. During the cleaning and disinfecting procedure, a chemical disinfectant is circulated through the flow path through which the dialysate normally flows during dialysis treatments. Heating the cleaning solution assists in killing microorganisms which might be transferred through the dialysis medium into the blood. It is typical that the temperature of the cleaning solution is relatively high, almost to the boiling point. A relatively significant amount of power is consumed to elevate the cleaning and disinfecting solution to a desirable temperature.
Heaters in dialysis machines are typically electric. In those geographic regions of the world where the typical commercial electrical service is supplied at 230 volts, an adequate amount of electrical power is generally available to heat the dialysate and the cleaning and disinfecting solution at an acceptable rate. However in those geographic areas where the commercial electrical service is supplied at 115 volts, the heating capacity of the heater is frequently limited enough to extend the length of the cleaning and disinfecting time, the warm-up period and even possibly the dialysis treatment time if the dialysate can not be heated at an adequate rate commensurate with the desired blood flow rate. While it is always possible to install a 230 volt electrical service, the cost of installation is frequently considered to be prohibitive.
Another contributing factor to the limited power delivery from heaters in dialysis machines is the safety regulations pertaining to dialysis machines. Generally, these regulations limit the amount of power that may be consumed by a dialysis machine to approximately 80% of the maximum power available from a typical single-circuit electrical service. Generally speaking, the typical single circuit electrical service is a 15 amp, 115 volt circuit. Consequently, of the approximately 1725 watts of available power, approximately only 1380 watts are available for use by the dialysis machine.
Not all of the power consumed by the dialysis machine is available for the heater. The other components of the dialysis machine require electrical power, such as the blood and dialysate pumps, cathode ray tube monitors, clamps and valves, and the system microcontrollers, among others. The amount of power available to the heater depends on how much power the other components use, because the function of these other components is essential to the performance of the dialysis treatment. From a priority standpoint, these other components, if in use during the treatment, must receive electrical power. Thus, since it is always possible to reduce the treatment flow rates without compromising the patient's safety, the available power to the heater has been limited to accommodate the other more critical components of the machine.
For example, the typical prior approach has been to predetermine the amount of power that each system of components within the machine will consume on a worst case basis. The worst case power consumptions are added, and the total is subtracted from the maximum allowed power consumption of the dialysis machine. The result is the amount of power available to the heater. The capacity of the heater is selected to provide that maximum amount of heat.
As a consequence of this approach to determining the capacity of the heater, the maximum amount of heat available for heating the dialysate is limited to the worst case consumption of all of the remaining components of the dialysis machine concerning their full allotted amounts of power. The practical reality is, however, that the other components very rarely if ever consume the maximum amount of power simultaneously. Nonetheless, because of the worst-case allocation approach to sizing the capacity of the heater, no additional power may be supplied for heating the dialysate.
It is with respect to these problems and other concerns and issues that the present invention has been developed.